Nothing. It's connected by a few centimeters.
You have the beautiful partition called as falx cerebri, which separates the cerebral hemisphere incompletely. This partition is made from the folding of the inner layer of the Dura mater. Dura mater is the outer covering of the meninges.
The falx cerebri separates the right and left hemispheres.
The falx cerebelli invaginates into the cerebellar notch between the two cerebellar hemispheres. It doesn't actually separate the two hemispheres though. The falx cerebri separates the two cerebral hemispheres.
Frontal Parietal Occipital Temporal Cerebellum
The cerebral hemispheres are connected by the corpus callosum.
There is one major fissure that divides the cerebral hemispheres, called the longitudinal fissure. It separates the left and right hemispheres of the brain.
The corpus collasum.
Dura mater extensions are found in the skull cavity. They are called the falx cerebri and the tentorium cerebelli. The falx cerebri runs vertically between the fissure in the cerebral hemispheres of the brain. The tentorium cerebelli runs between the cerebellum and the occipital lobes.
it separates the cerebrum into left and right hemispheres.
Longitudinal Fissure the longitudinal fissure
corrus collasum
medulla oblanga